USB midi noise connecting to Morningstar MC6 pro

[valeriodaniele]

Hi all,

I use an MC6 Pro to send MIDI to the MetaModule. Everything works great, except for a high-pitched ground loop noise that appears as soon as I connect the two devices.

I wonder if this is happening because the MM (host) is powering the MC6 Pro. I noticed that the noise increases significantly if I disconnect the external 9V power supply from the MC6 Pro.

Is there a way to turn off power output from the MetaModule’s USB-C port? Alternatively, can anyone recommend a USB noise isolator/filter to insert between the two devices?

[TheTechnobear]

usb (host) does not supply power if the device doesn’t request it, which it wont if connected to the mains.

ground loops only occur if 2+ devices are connected to mains (that’s the loop), so should not occur if you do not use external power. (unless, you have other devices attached to the mains)

the other noise polluter, would be switching noise… that occurs regardless of power.

does the usb cable you use have a ferrite choke (or 2) on it?
this helps for switching noise (but not ground loops)

any good quality USB cable with chokes would be good,
(you can also add ‘external’ chokes to a cable)

[valeriodaniele]

Hi, thanks for clarifying… I suspect it might be switching noise, especially because it’s a subtle squeal with no low-end noise.
My cable is quite good, but I’ll try adding some ferrite chokes and let you know!
Thanx!

[valeriodaniele]

Hi all,
connecting in new Device Mode (with the new firmware, midi coming from midi host port on the MC6pro) noise is gone!
The strange thing is that in that way only one kind of CC messages is not sent. It’s a CC waveform generator sent by the MC6 pro. I use it to make a kind of slow rising of one parameter in my MM preset.
If I connect in Host mode the message is perfectly sent… in Device mode the message is not sent
Any idea??

[valeriodaniele]

Hi @danngreen, sorry to bother … have you got any idea or explanation for the behavior described?

[danngreen]

It sounds like 3 distinct problems: a CC isn’t being sent, noise when powering the MC6, and noise when MC6 is powering itself.

CC
There shouldn’t be any difference between Host and Device mode, the paths are the same on the MetaModule. I would probably try to track down why that one CC is not getting sent by making a new patch, adding any module, and then start to create a new MIDI mapping to one of the module’s knobs. In that pop-up you will see what MIDI message the MetaModule is receiving. Perhaps the MC6 is sending it over some different channel or doing something else unexpected.

Device mode is pretty new in the firmware, so it’s possible we’re seeing some bug in the firmware but it’d be strange for it to just filter one CC. Try changing the CC number, the MIDI channel, try other MIDI signals and see what gets through. I’m able to get CCs on all channels, when sending from VCV Rack on my computer. Try that and make sure the CC + channel you’re expecting can make it from a different source.

Powering the MC6 with the MetaModule
As for the noise when you’re using the MetaModule to power the MC6, is the MC6 connected to anything else besides the MetaModule? I would suspect ground loops if so. If not, then if it were on my bench I would poke around the power supply rails. I looked at the specs and the unit draws 330mA (or more if other thing are connected to it). That’s on the high side, though safe because the MM can supply 500mA. Ultimately the USB VBUS 5V is generated from the +12V rail, it’s possible the increased load on the rails is causing noise somewhere.

If you have access to a scope you could probably probe the +5V USB supply (I can show you where to probe), and the +12V eurorack power supply rails to see where the noise is coming from. The power supply for the audio path on the MetaModule is completely separate from the USB VBUS supply, so it’s unlikely a taxed VBUS would bleed over to the audio, I would think some sort of ground issue is more likely, but these kinds of issues can be complex. Keep in mind whatever’s powering your speakers and mixer any other gear in the signal path is also part of the equation.
If you happen to have a battery powered headphone amp, plugging that into the MetaModule’s output and listening for noise will tell you something.

Separate power supply for the MC6
As for when you power the MC6 with its own power supply, and connect the MetaModule in Host mode, if the MC6 is USB-compliant then the MetaModule will not turn on VBUS. I’ve seen one non-compliant self-powered USB device (from a well-respected, major manufacturer) that does something scary: it requests VBUS power from the Host, and then physically connects the incoming VBUS to its own internal 5V power supply. So two power supplies are feeding into each other and battling it out. Hopefully the MC6 doesn’t do this! But if it does, then that’s your noise right there.

[valeriodaniele]

Hi Dan, thank you.

CC: Got it. I’ll try with a new patch and change the CC number and channel as well. I’ll keep you posted.

Powering MC6 via MM: Yes, the MC6 is connected to several other devices. However, that’s not an issue at all since I don’t intend to power it via the MM—I prefer using a dedicated power supply for the MC6 anyway.

Separate Power on MC6: two currents together??? I really hope that’s not the case…

Device Mode: Connecting in Device Mode works perfectly for me, especially since it completely eliminates the noise. The only thing left to figure out is why a rising CC value sent via a Waveform Generator isn’t being received specifically in Device Mode. Just to clarify, all other “static” CC values are received with no issues.